Extreme pressure lubricating additive

ABSTRACT

COMPOSITIONS COMPRISING A CLASS OF SULFIDIZED-PHOSPHOSULFIDIZED ESTERS IMPART EXTREME PRESSURE AND ANTI-WEAR PROPERTIES TO LUBRICATING OILS.

"United States Patent Ofiice 3,775,322 Patented Nov. 27, 1973 ABSTRACT OF THE DISCLOSURE Compositions comprising a class of sulfidized-phosphosulzfidized esters impart extreme pressure and anti-wear properties to lubricating oils.

BACKGROUND OF THE INVENTION Field of the invention The control of friction and wear under high load conditions requires boundary lubrication. Boundary lubrication appears to depend on the properties of the lubricant other than its viscosity. Boundary lubrication can be achieved by the formation of films on the metallic surface. While the formation of such film is thermodynamically favored, the thickness of the surface film ranges from a fewhundredths of a microinch for single molecule layers of adsorbed gases to several dozen microinches for thick films from oils with extreme pressure (E-P) additives. A problem in the lubrication art is to provide a boundary film with the proper chemical and physical characteristics to control friction and/ or wear under high load conditions, and the correct chemical properties to avoid detrimental damage to the surface and other disadvantageous effects such as toxicity, oxidation catalysis and sludge deposition.

Lead nephthenate has often been used in conjunction with sulfidized compounds to produce lubricating compositions with extreme pressure and anti-wear properties. However, the lead naphthenate compositions contain all of the disadvantages heretofore discussed. Thus, an object of this invention was to find extreme pressure and antiwear agents to replace lead naphthenate-sulfur compound compositions. It was found that this object is achieved by certain sulfidized-phosphosulfidized esters of fatty acids and alkanols.

SUMMARY Extreme pressure, anti-friction and anti-wear additives for lubricating oils are prepared by sulfidizing and phosphosulfidizing fatty acid esters of a C -C fatty acid and a (l -C alkanol or alkenol. The fatty acid ester can be the tallate obtained from the esterification of derosinified tall oil. An unusual and novel improvement of the present invention comprises the high degree of sulfidization which is at least one equivalent of sulfur per equivalent of C=C (ethylenic double bonds) in the ester. The additive when present at only the 4-5 percent level is found to impart both extreme pressure and anti-wear properties to the lubricating oil. Timken test maximum load values increased from pounds (without additive) to over 60 pounds (with additive) and scar diameters in the-Four- Ball test are reduced substantially. Thus the load-carrying capacity of lubricating fluid is materially improved without excessive and increasing amounts of wear at the higher percentages of sulfur incorporated in the present additive.

DESCRIPTION OF THE INVENTION This invention is concerned with a novel class of oiliness agents which are prepared by highly sulfidizing a fatty acid ester of a C C fatty acid and a C -C alkanol or alkenol.

Examples of the fatty acid include unsaturated monoethenoid acids such as oleic acid, C H COOH, palmitoleic acid, C H COOH, petroselinic acid, C H COOH, erucic acid, C H COOH, gadoleic acid, C19H3'1COOH, vaccenic acid, C H OOOH, and other naturally occurring and synthetic acids of the general formula:

and unsaturated polyethenoid acids such as linoleic acid, C H COOH. Also included are saturated acids such as n-undecanoic, C H OOOH, lauric acid, C 'I-I COOH, myristic acid, C13H27COOH, palmitic acid, C H COOH, stearic acid, C H COOH, and other naturally occurring and synthetic acids of the formula: C H COOH. Branched-chain fatty acids are also included, as Well as substituted acids such as ricinoleic acid, C H 'OHCoOH.

Examples of the alcohols which find use within the scope of the present invention are methyl alcohol, propyl alcohol, butyl alcohol, hexanol, octanol, undeeanol, tetradecanol, etc. Monoethenoid and polyethenoid oils are also included, such as l-hydroxy-3-hexene, Z-hydroxy-S, 7- dodecadiene, 1-hydroxy-4, 7-pentadecadiene, 2-hydroxy- 10-dodecosene, etc. The alcohol can be straight chain or branched chain or partially branched and partially straight-chain alcohols. Substituted alcohols are also included, such as the 1,2-g1ycols, 1,3-glycols, etc, as Well as the polyols.

A particularly preferred embodiment of this invention is the product of the reaction of oleic or linoleic acid with a C -C alcohol, such as undecyl alcohol. One mole of this ester product is then sulfidized with one or more moles of sulfur, depending upon the average number of double bonds present in the ester. It is an essential element of the invention that either the alcohol or the fatty acid be unsaturated. This is necessary for elfective sulfidation. Although the usefulness of these materials as lubrieating additives is independent of any particular supposition about the structure of the sulfidized product, it is believed that the sulfidation step introduces sulfur by forming linkages with -(S),,- between ethylenic double bond positions. Thus, it is believed that either the alcoholic or acidic portion of the ester molecule must be unsaturated to form effective linkages with other molecules.

The esters within the scope of the present invention are illustrated by isopropyl oleate, ethyl linoleate, pentadecyl oleate, eicosyl linoleate, decenyl stearate, eicosenyl laurate, propyl linoleate, pentadecenyl linoleate, undecyl, ricinoleate, pentadecyl tallate, etc.

Tall oil is a by-product of the sulfate process for the manufacture of wood pulp. It consists of about percent resin acids. The resin obtained from various species of pine is called rosin, which is chiefly abietic acid,

The remaining 50 percent of tall oil consists of unsaturated fatty acids, chiefly oleic and linoleic acids. Thus, derosinified tall oil is a convenient source of these unsaturated acids. Rosin is a source of the undesirable auxiliary properties of lube oil additives mentioned earlier when it is present in high percentage in tall oil prior to neutralization and/or sulfurization. Derosinified tall oil is commercially available. For use in embodiments of the present invention, the derosinified tall oil contains less than percent of rosin.

In a preferred embodiment of the invention, derosinified tall oil is reacted with an alkyl alcohol and sulfidized to the extent of 30 percent of sulfur by weight. Concurrently, or sequentially, the sulfidized ester is phosphosulfidized by reaction With sufficient P 8 to supply 0.1-2 percent phosphorus in the final product.

METHOD OF PREPARATION The ester substrate may be prepared by any of the well-known methods. Typically, as described in the following example, the ester is prepared by heating an unsaturated carboxylic acid, such as oleic acid, with a slight excess of an alcohol, such as lauric alcohol, in the presence of a catalyst, such as sulfonated polystyrene. The product should contain one to two double bonds per molecule to provide suitable capacity for reaction with sulfur and phosphorus pentasulfide.

The unsaturated ester is preferably heated with sufficient sulfur and phosphorus pentasulfide to convert it to a mixture of mainly dithioethers and trithioethers, with small portions of thiophosphonates and thiophosphates. The reaction temperature should be about ISO-180 C. and the time in inverse order to temperature, from 20-5 hours. A nitrogen sparge is useful for removing small quantities of hydrogen sulfide that form as by-product. Otherwise, no further treatment is necessary.

EXAMPLE 1 290 grams of tall oil (Arizona Chemical Company, Acintol FA-1 Specia 189 grams of n-undecanol (Gulf Oil), and 10 grams of polystyrenesulfonic acid resin (Rohm & Haas Company, Amberlyst were stirred at 128-132 C. under nitrogen with condenser and water receiver for 5 hours and the resin catalyst was then filtered off. The product was 428 grams of a tan oil with an acid number of 5 mg. KOH/g.

EXAMPLE 2 To a 2-liter, 3-neck flask was charged 880 grams (about 2 moles) of tallate of a C -C alkanol, 128 grams (about 4 moles) of sulfur and 11.1 grams (about 0.05 mole) of P 8 The mixture was stirred under nitrogen to about 175 C. for 25 minutes. The mixture was maintained at l72176 C. for 6 hours with stirring and nitrogen bubbling through the mixture. The dark-brown reaction product was filtered hot (130 C.) and weighed 984 grams. Percent sulfur was 12.6 (theoretical 13.3). Percent phosphorus was 0.31. Percent active sulfur was 2.6 (ASTM D662-66T).

EXAMPLE 3 880 grams (about 2 moles) of alkyl tallate, formed from the reaction of a mixture of dodecanol and tridecanol with derosinified tall oil, was sulfidized with 128 grams (about 4 moles) of sulfur. The reaction occurred at a temperature of 169-78 C., for six hours. 994 grams of dark oil were obtained as a product. The product contained 12 percent sulfur by weight and 1.5 percent active sulfur by weight, defined by ASTM D1662-66T.

EXAMPLE 4 707 grams (about 1.6 moles) of C -C alkyl tallate of Example 2 was sulfidized with 113 grams (about 4.1 moles) of sulfur and phosphosulfidized with 8.9 grams (about 0.042 mole) of P 8 ADDITIVE MEDIUM The compounds of this invention may be used singly or preferably in combinations of two or more in an oil of A lubricating viscosity. The lubricating oil can be any relatively inert and stable fluid of lubricating viscosity. Such lubricating fluids generally have viscosities of 35-50,000 Saybolt Universal seconds (SUS) at 100 F. The fluid medium or oil may be derived from either natural or synthetic sources. Included among the natural hydrocarbonaceous oils are paraffin-base, naphthenic base, or mixed base oils. Eynthetic oils include polymers of various olefins, generally from 2 to 6 carbon atoms, alkylated aromatic hydrocarbons, etc. Non-hydrocarbon oils include polyalkylene oxides, aromatic ethers, silicones, etc. The preferred media are the hydrocarbonaceous media, both natural and synthetic. Preferred are those hydrocarbonaceous oils having viscosity of about IOU-4,000 SUS and particularly those having viscosity from 200 to 2,000 SUS at 100 F. The compounds of this invention may also be used singly, or preferably in combinations of two or more in lubricating greases. Greases comprise oils thickened by gellants or thickeners which are lithium, sodium, and calcium soaps, or snythetic soap-like salts, non-carboxylic salts, polymers, various inorganic compounds, petroleum oils and polysiloxanes.

Lubricating oil or grease will be present at or greater percent by weight of the final lubricant composition. In concentrates, however, the oil may be present as 10-75 percent by weight. These concentrates are diluted with additional oils prior to being placed in service to obtain the requisite concentration.

Other additives may also be present in the composition of this invention. Materials may be added to enhance the EP effect of the additive or provide some other desirable properties to the lubricating medium. These include such additives as rust and corrosion inhibitors, anti-oxidants, oiliness agents, detergents, foam inhibitors, anti-wear agents, viscosity index improvers, pour point depressants, etc. Usually these will be in the range of about 0-5 percent by weight, more generaly in the range of from about 0-2 percent by weight of the total composition.

Typical additional additives found in compositions of the present invention include phenolic and arylamine antioxidants, zinc dihydrocarbyldithiophosphates, rust inhibitors, such as the metal sulfonates and foam inhibitors such as the polyethyl siloxanes, etc.

EXAMPLE 5 A lubricating composition was compounded from 4.7 percent by weight of the product of Example 2 and 95.3 percent by weight of a base oil consisting of 70 parts by weight of 150 SUS at 210 F. bright stock and 26 parts by weight of 350 SUS at 150 F. neutral oil. The resultant composition had a viscosity of 1500 SUS at F. and

a percent sulfur by weight of 0.6 percent of the total lubricating composition.

EXAMPLE 6 7.9 weight percent of the additive of Example 2 was blended with 92.1 weight percent of the base oil of Example 5 to yield a lubricating composition having 1.0 percent sulfur by weight of total composition.

EXAMPLE 7 2.3 weight percent of the additive of Example 3 was blended with 97.7 weight percent vof the base oil of Example 5 to yield a fluid composition containing sulfur to the extent of 0.3 percent by weight of total composition.

EXAMPLE 8 4.5 percent of the additive of Example 3 was blended with 95.5 percent by weight of the base oil of Example 5 to yield a fluid composition. containing sulfur to the extent'of 0.6 percent by weight of the total composition.

EXAMPLE 9 7.5 percent by weight of the additive of Example 3 was blended with 92.5 percent by weight of the base oil of Example 5 to yield a fluid composition containing sulfur to the extent of 1 percent by weight of total composition.

LUBRICANT PERFORMANOE The load-carrying capacity of the lubricating fluids of Examples 5-8 and the base oil was tested by means of the Timken Extreme Pressure Test (ASTM D2782-71) and the Four-Ball wear test (ASTM D2266-67). These tests are widely used for specification purposes and differentiate between lubricating fluids having low, medium, and high levels of extreme pressure properties. In the Timken test a steel cup is rotated against a steel block. The rotating speed is 800 r.p.m. and fluid samples are preheated to 38 C. before starting the test. Two determinations are made: the minimum load value which will rupture the lubricant film being tested between the rotating cup and the stationary block and cause abrasion, and the maximum load at which the rotating cup will not rupture the lubricating film and cause abrasion between the rotating cup and the stationary block. Thus, the Timken test defines the load carrying capacity of a lubricant as the maximum load or pressure which can be sustained by the lubricant .when used in a given system under specific conditions without failure of moving bearings or sliding contact surfaces as evidenced by seizure or welding. Seizure or welding is evidenced by streaks appearing on the surface of the test cup, an increase in friction and wear, or unusual noise and vibration. Comparative results of lubricants containing additives of the present invention and the base oil in the T imken test are given in Table I.

It is critically important for the purposes of the present invention that the fuel lubricating composition pass the 60-pound Timken test, without excessive wear, in order to meet the requirements of the U5. steel industry and other industrial users of extreme pressure gear oils. It has been found that the P18 ratio, the total percent S and the ester structure itself are critical factors in meeting these requirements. Additionally, if the formula tion is to be used with copper, or copper alloy metals, then the percent active sulfur, as measured, for example, in ASTM D1662-66T, should not rise above a few percent.

TABLE L-TIMKEN TEST Minimum load, lbs. load, lbs.

In the Four-Ball test a steel ball'rotating at 1800 r.p.m. under a load of 20 kg. is held against three stationary steel balls in the form of a cradle. The lubricating fluid is brought to 75 C. and rotation occurs for a period of one hour, after which the diameter of scars on the rotating ball is measured. In the Four-Ball test the load carrying property of the lubricating fluid is measured as the ability of a lubricant to prevent wear at applied loads. Four-Ball test data for lubricating fluids of Examples 5-8 and the base oil are presented in Table II.

TABLE II Four-Ball Test The results of Table I show that excellent Timken load values are obtained at the high percentages of sulfur utilized in the present invention. The results given in Table II, on the other hand, show that this high level of sulfurization, quite surprisingly, does not degrade the antiwear properties of the lubricating fluid, but enhances them.

It was found that the desired 60-pound Timken test load was not achieved without the phosphosulfidation of the sulfidized ester. At least 0.1 percent phosphorus is required in the sulfidized-phosphosulfidized ester in order to achieve both passable Timken test and Four-Ball test values.

A particular advantage in the use of sulfidized esters is shown by comparison with similar levels of sulfidation in olefins, specifically cracked wax olefins, i.e., C -C alpha olefins. At levels of 1 percent of sulfur in the total composition the sulfidized and phosphosulfidized cracked wax olefins give maximum Timken loads of only 40-50 pounds. While at lower levels of sulfur, the Timken maximum load carrying properties of cracked wax olefins range from 3050 pounds. Similarly, the sulfidized cracked wax olefins give excessive and increasing amounts of wear at higher percentages of sulfur as represented in the Four- Ball test, scar diameters ranging from 0.4 mm. at 0.6 percent sulfur to 0.65 mm. at 1 percent sulfur in the oil blend.

What is claimed is:

1. A highly sulfidized lubricating composition consisting essentially of a major amount of lubricating oil or grease, and from 1 to 10 percent by weight of the total lubricating composition of a sulfidized-phosphosulfidized ester of a C -C fatty acid and a C -C alkanol or alkenol, wherein the fatty acid and/or alcohol is unsaturated, and the sulfidized-phosphosulfidized ester contains from 10 to 20 percent by weight sulfur and from 0.1 to 1 percent by weight phosphorus.

2. A highly sulfidized lubricating composition consisting essentially of a major amount of lubricating oil or grease, and from 1 to 10 percent by weight of the total lubricating composition of a sulfidized-phosphosulfidized ester of derosinified tall oil and a C C alkanol or alkenol, wherein said ester contains from 10 to 20 percent by weight sulfur and from 0.1 to 1 percent by weight phosphorus.

3. A lubricating composition according to claim 2, wherein the alkanol is a C -C alkanol.

4. A lubricating composition according to claim 2, wherein said ester contains less than 3 percent ASTM D1662-66T active sulfur.

References Cited UNITED STATES PATENTS 3,182,022 5/1965 Siegart et al. 25246.6 2,274,025 2/1942 Yule 252-46.6 2,483,600 10/ 1949 Stucker etal. 25246.6 2,929,778 3/1960 Manteuifel 25246.6 X 3,455,844 7/ 1969 Beare et a1 25246.6 2,873,254 2/1959 Wolfram et al. 252'46.6 2,820,013 l/ 1958 Chapman et al 252-46.7 2,179,061 11/1939 Smith.

FOREIGN PATENTS 530,902 9/ 1956 Canada 252-46.6

DANIEL E. WYMAN, Primary Examiner H. M. S. SNEED. Assistant Examiner 

